Staunton, VA Twin Flash Floods of August 2020

In the month of August, there were several flooding rainfall events across the forecast area. Perhaps hardest hit during this time was the city of Staunton, VA in Augusta County. During the month of August, Staunton experienced 2 significant flash flood events exactly 2 weeks apart. The first of which occurred on Saturday August 8th, and the second occurring on Saturday August 22nd. 

August 8th

The setup for this day was relatively benign across much of the area. High pressure was beginning to push in from the west throughout the day, while a slow moving surface front lingered just south of the area. Additionally, there was a pressure trough located along the Blue Ridge that was nearly stationary. That, paired with the terrain circulations in the mountains lead to the development of an isolated shower just northwest of Staunton, VA around 4:00 PM EDT. The shower would gradually move south and east towards Staunton throughout the evening, but very slowly, owing to the lack of any significant steering flow aloft. The shower strengthened as well, becoming a thunderstorm into the evening with some very heavy rainfall. Around 8:30 PM EDT, the storm arrived in Staunton, and would sit there for the next couple of hours, dumping heavy rainfall over the city. By 11:15 PM EDT, the storm had weakened, leaving only light rain in the area. Precipitation estimates from the KLWX doppler radar were around 2-3 inches over Staunton. However, these are generally way overdone due to the radar being blocked in that area. Localized amounts of 6 inches or more were observed according to some public observations, with the worst hit area being the northwest side of town. 

Below is an image of the estimated rainfall from the flash flood event on August 8th.

August 22nd

The flash flood event that occurred on August 22nd differed significantly from the August 8th event in terms of the overall setup, but came with similar impacts to the City of Staunton once again. An area of upper-level low pressure was centered to our southwest. Meanwhile, at the surface, a surface low was strengthening over the southeast U.S. with the warm front extending into central Virginia. Heating early in the day north of the front lead to the development of a differential heating boundary across the area, which aided in thunderstorm development along and west of the Blue Ridge, especially after 2:00 PM EDT. The region was located underneath the left exit region of the upper jet, which acted to enhance thunderstorm development through the afternoon/evening. Additionally, the warm front was drifting northward throughout the afternoon/evening as well, adding more fuel to the fire. Convection really started to explode by 4 or 5 PM EDT, moving into the Staunton area. Storm motions with this event were generally much faster with this event. However, one storm started over Staunton around 4:15 PM EDT, and sat there for several hours before moving out around 7:15 PM EDT. This storm appeared to get locked onto the Blue Ridge and just didn't want to budge. However, this would not be the end of rain for Staunton, as another thunderstorm moved in between 8 and 9 PM EDT, dumping even more heavy rain, especially southeast of town. There was then another hour or so of moderate stratiform precipitation behind the main line before rain moved out of the area around 10:30 PM EDT. In all, radar estimated anywhere from 2-4 inches of rainfall across the City of Staunton. As mentioned before, radar estimates here are generally low due to beam blockage issues. Locally higher amounts over 6 inches likely fell here once again. 

Below is an image of the estimated rainfall from the flash flood event on August 22nd. 

While our forecast area is no stranger to flash flooding events, what made this event rather historic was the fact that two high profile flash floods occurred just 2 weeks apart in the same location. The city of Staunton received over a foot of rainfall in the month of August from just these 2 systems alone.